1. Field of the Invention
This invention relates to processes and apparatus for extraction of oil from a moving bed of carbonaceous materials such as oil shale.
2. Description of the Prior Art
Systems for retorting a moving bed of oil shale supported on a traveling grate by passing heat transfer gas streams through the bed to transfer heat directly to the shale are disclosed in such U.S. patents as 3,325,395 to Ban; 3,560,369 to Rowland et al; 3,644,193 to Weggel et al and 3,475,279 to Bowman. The systems disclosed in such patents, in general, educt oil from the shale at only one temperature and are incapable of: (1) extracting from the shale different weight fractions of oil unmixed with the combustible products; (2) controlling the type of oil educted from the shale; (3) removing a pollutant such as hydrogen sulphide from the shale; or (4) removing a gaseous chemical feedstock such as ethylene from the shale.
The system of the 3,644,193 patent is incapable of separating different weight fractions of oil from the shale particles. The system of the U.S. Pat. No. 3,560,369 patent requires crushing, grinding and screening of the oil shale to segregate the fines; agglomerating the fines with a binder such as heavy oil; and then forming a bed on the traveling grate with the agglomerated fines occupying a middle layer between upper and lower layers of larger shale particles. The rate of transfer of heat from the radiant heaters of U.S. Pat. No. 3,475,279 to the shale particles is very low in comparison to a moving bed system wherein a heated gas steam is passed through the moving shale bed, and both retorting and sintering of the coal or shale particles occur in the same zone in this patent which does not permit close control of the temperature to which the particles are heated and also results in mixing of the desired volatile products with the combustion gases and cracking of the hydrocarbons. Ambient air rather than a nonoxidizing or neutral gas is passed through the moving shale bed in the second, or sintering zone of the traveling grate system shown in FIG. 4 of the U.S. Pat. No. 3,325,395 and burned with the carbon in the shale particles. Such arrangement does not permit control of the oil fraction educted and also mixes the combustion gases with the desired condensable products.
Rotary kiln systems for tumbling and retorting a bed of oil shale particles are disclosed in such U.S. patents as 1,383,205; 1,423,716; 1,717,786; 2,441,386; 2,664,389; 3,496,094 and 3,844,929, but such rotary kiln shale retorting systems are incapable of separating different fractions of oil from the shale and have the disadvantages that the shale particles can only occupy a small portion of the kiln cross section, e.g., 14 percent, with the result that the tonnage capacity per unit size of apparatus is relatively low and that combustion and retorting occur in the same vessel, which results in low efficiency and in at least partial cracking of the hydrocarbons within the kiln.